v3.26.3
Cover
Nov. 05, 2026
Document Information [Line Items]  
Document Type 8-K
Amendment Flag false
Document Period End Date Nov. 05, 2026
Entity File Number 001-43039
Entity Registrant Name BLACK SPADE ACQUISITION III CO
Entity Central Index Key 0002087087
Entity Tax Identification Number 00-0000000
Entity Incorporation, State or Country Code E9
Entity Address, Address Line One Suite 2902, 29/F, The Centrium
Entity Address, Address Line Two 60 Wyndham Street
Entity Address, City or Town Central
Entity Address, Country HK
Entity Address, Postal Zip Code 00000
City Area Code 852
Local Phone Number 3955 1316
Written Communications true
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Emerging Growth Company true
Elected Not To Use the Extended Transition Period false
Class A ordinary shares, $0.0001 par value, included as part of the units [Member]  
Document Information [Line Items]  
Title of 12(b) Security Class A ordinary shares, $0.0001 par value, included as part of the units
Trading Symbol BIII
Security Exchange Name NYSE
Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50, included as part of the units [Member]  
Document Information [Line Items]  
Title of 12(b) Security Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50, included as part of the units
Trading Symbol BIIIW
Security Exchange Name NYSE
Units, each consisting of one Class A ordinary share and one-third of one redeemable warrant [Member]  
Document Information [Line Items]  
Title of 12(b) Security Units, each consisting of one Class A ordinary share and one-third of one redeemable warrant
Trading Symbol BIIIU
Security Exchange Name NYSE